[volt-nuts] Offset voltage temperature drift in rail-to-rail opamps

[Attila Kinali]

Hi,

I am currently looking at the LT1677/1678/1679 family of opamps, which
have an increadibly low tempco for the input offset voltage (0.4µV/°C typ).
Ie they are not that far of from chopper/auto-zero opamps (only a factor
of 20-50), but with a quite a bit lower noise. And more imporantly,
they do not have the noise peak in the 0.1-10MHz region these zero-drift
opamps are plagued with. 

But, when the input voltage comes close within the upper or lower rail,
the input offset voltage specs get much worse. Which is ok, as I am 
not so much interested in the absolute offset as its drift.
But is my assumption correct, that with worse offset spec, close to the
rails, also the offset voltage drift specs get worse?

Another question I have is, whether I am just fooling myself with
the noise spec. If I am mainly interested in the noise performance
in the range between 0.1Hz and 100Hz (maybe even just up to 10Hz),
are the LT167x a good choice? Or should I rather stick to the LTC2057?

(Yes, there is still the option of using an LT1677 and an LT2057 to 
compensate its offset. But I don't want to go that way due to the
increase of complexity...at least not yet)

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
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use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson